The invention relates to a stringed instrument having a sound box, which is bounded upwardly by a top board and downwardly by an arched or planar bottom wall, in which the top board carries a string-supporting bridge and within the sound box are provided at least one lever at right angles to the direction of the strings and a supporting element, in order to transfer joint vibratory movements of the top board in phase-displaced manner to the bottom wall.
U.S. Pat. No. 5,542,329 discloses an instrument of this type, in which the lever and supporting elements provided within the sound box have the function of transferring vibrations acting from the strings, via the bridge onto the sound box top board from the latter to its bottom wall in such a way that the latter performs an oppositely directed or phase-displaced vibratory movement. This has the advantage that the pumping action of the top board acting inwardly on the air in the sound box is supplemented by the consequently simultaneously inwardly directed pumping movement of the bottom wall. However, it is disadvantageous that the sound box required stiffening ribs limiting its vibration capacity in order to absorb the elastic or tensional forces of the strings acting thereon via the bridge. It is also disadvantageous that the oscillations of the top board are only transferred through the components from one position to the bottom wall, so that tilting movements of the bridge in a direction at right angles to the strings lead to deformations to the top board, which have a disadvantageous influence on the sound evolution of the instrument.
The problem of the invention is to provide a stringed instrument of the aforementioned type which, whilst retaining a traditional external shape of the sound box, has a fuller and richer sound. The top board of the sound box, without overloading by the elastic force of the playing strings can be made thinner and therefore more vibratable and the bottom wall of the sound box can perform a relatively large vibratory movement opposing the vibration of the top board.